Method and azimuthal probe for localizing the emergence point of ventricular tachycardias

ABSTRACT

Device permitting localization of the emergence point of ventricular tachycardias in cardiological medicine, characterized, in comparison with traditional cardiac mapping, by: a precision of the same order, its speed of use, its low cost and the further possibility of localizing the macro-re-entry pathway (around aneurysms, for example). 
     In distinction to traditional mapping, this device dispenses with the construction of a map of isochrones (14). 
     The principle of the device according to the invention is based on localization of the propagation of the myocardial cell depolarization, or of the muscle contraction of the heart (15) which results directly therefrom. This localization is carried out in stages (17) over the length of its pathway (13) from an arbitrary point (16) on the heart chosen by the operator, retracing this pathway as far as its source (12&#39;), which is referred to as the emergence point.

The present invention relates to a device permitting localization of theemergence point of ventricular tachycardias in cardiological medicine,by a successive approach method, characterized, in comparison withtraditional cardiac mapping, by: a precision of the same order, itsspeed of use, its low cost and the further possibility of localizing themacro-re-entry pathway (around aneurysms, for example).

In distinction to traditional mapping, this device dispenses with theconstruction of a map of isochrones.

The techniques currently used are either manual or automatic, and areapplied to the epicardium, the endocardium or the myocardium itself: A)Epicardium/Manual method: a three-pole probe is moved on the surface ofthe heart, while a reference electrode is attached close to the base ofthe aorta.

An electrocardiograph comprising:

a trace for the surface ECG,

two traces for the reference electrocardiogram and that of the mobileprobe,

enables the horizontal distance on the paper between the deflections tobe measured at the time which has elapsed (interval) between thedepolarizations perceived by the reference electrode and the mobileelectrode.

Several interval values enable a map of isochrones (equal intervalcurves) to be constructed, giving a two-dimensional view of thepropagation of the depolarization. The point on this map correspondingto the shortest interval is considered to be the emergence point, whichis accordingly subjected to surgical removal. This removal may becarried out by ventriculotomy with a scalpel, by diathermy or by acryosurgical technique.

B) Epicardium/Automatic method: an epicardial net supports from 50 tomore than 300 electrodes each connected to an instrumentation amplifier.Each route is multiplexed, sampled/blocked and converted to digitalform. A processor acquires these data, processes them and displays themon a monitor or printer in list or image form.

C) Myocardium: a needle equipped with several electrodes providesinformation about the depth of the emergence point in the thickness ofthe myocardium.

D) Endocardium/Manual method: a catheter is positioned at differentpoints of the endocardium. The location corresponding to the earliestinterval, relative to the reference catheter, is subjected tofulguration.

E) Endocardium/Automatic method: an endocavitary inflatable ballooncontaining several tens of electrodes permits localization of theemergence point using the acquisition system described in B).

The principle of the device according to the invention is based onlocalization of the propagation of the myocardial cell depolarization,or of the muscle contraction of the heart which results directlytherefrom. This localization is carried out in stages over the entirelength of its pathway from an arbitrary point on the heart chosen by theoperator, retracing this pathway as far as its source, which is referredto as the emergence point.

The device according to the invention comprises a probe connected toelectronic circuits which are designed to process the signals gatheredby the probe and to control a device/operator interface. The deviceaccording to the invention is referred to as an "azimuthal probe", thetwo words not being separated in this case. The term "probe" is reservedfor an assembly comprising the sensors, their support, the electricallinking cable with its connector and any means of signalling which areattached thereto and intended for the operator.

The probe is composed of at least one assembly of two sensors sensitiveto myocardial depolarization (electrochemical phenomenon) or to cardiaccontraction (mechanical phenomenon which is the consequence thereof).Each assembly of two sensors is arranged on an approximately rectilinearaxis. The sensors are attached to a support which the operator movesover the epicardium or over the endocardium.

The azimuthal probe enables the following to be determined:

the sense of the propagation of the myocardial cell depolarization or ofthe cardiac muscle contraction which results directly therefrom, thecommon source of which is the activation of the emergence point; thissense is determined along the direction represented by the axis of thetwo sensors, when the operator can note the order of arrival of theactivation potentials under one sensor and then under the other (phaseshift); if these arrivals are simultaneous, the phase shift is zero;

the direction of this propagation, by several phase shift measurementsas above, when the probe is rotated about an axis passing between thetwo sensors and perpendicular to the cardiac surface; the direction isdetermined, either when the operator can note the maximum phase shift,the axis of the sensors then being coincident with the direction, orwhen the operator can note a zero phase shift, the axis of the sensorsthen being perpendicular to the direction;

the pathway of the depolarization, starting from an arbitrary point onthe heart, and carrying out at each stage a determination of sense anddirection as described above, followed by a movement of the probe on orin the heart by a distance of the order of one centimeter, to bedetermined by experience, in the opposite sense and in the directionwhich have just been determined.

The emergence point is reached after several stages as just described.This point is recognized by the fact that the depolarization ispropagated centripetally from it. The phase shifts measured at thispoint are hence all zero.

With the object of improving the azimuth discrimination during one andthe same measurement, the assemblies of two sensors are combined on asingle probe according to two or more directions. Each assembly ofsensors provides information which is transmitted to the operator. Theuncertainty ε about the direction is calculated by: ##EQU1## where: ε isexpressed in degrees

n=number of groups of two sensors

To avoid the multiplication of sensors, the device comprises, in animproved version, only two assemblies of two sensors arranged accordingto two perpendicular axes. Each assembly provides two signals combinedin one phase-shift signal. Each phase shift, transferred to anorthonormal reference system, is considered to be the projection of avector on this reference system. This vector coincides approximatelywith the azimuth of the depolarization. The vector indicates the senseand direction in which it is necessary to move in order to carry out thenext stage of measurement.

Incidentally, the operator can then localize the depth of the seat ofactivation of the tachycardia by pushing in, in successive stages, aneedle comprising an assembly of two sensors, at the location previouslydetermined, namely the emergence point. This point is, in fact, theelectrical projection of the seat of activation, on the endocardium orepicardium according to the route first used by the operator. The seatof activation is found when the phase shift between the two signalsrecorded by the sensors is zero (no preferential senses). There is noneed for the direction to be determined by the device, since it isrepresented by the axis of the needle. In a second step, the operatoremploys a means of destruction of the region thus localized, theoperation of which is authorized by the device and the active portion ofwhich is located on the needle. By way of example, this active portioncan be:

a group of electrodes conveying an electric current produced by ahigh-frequency diathermy generator (electric scalpel) or a cardiacdefibrillator,

a heat resistor,

a duct carrying a refrigerant fluid (cryosurgery).

The device according to the invention comprises electronic circuitsdesigned to process the signal provided by the sensors, to providesignals carrying the desired information (azimuth of the depolarizationand location of the emergence point), and optionally to control adestruction device, internal or provided by the user. Each sensor isfollowed by a processing circuit comprising an amplifier, a filterdesigned to select the useful component of the signal and hysteresiscomparators converting the analogue signals to binary logic signals.This circuit is referred to as a "channel". The channels are grouped inpairs, corresponding to the assemblies of two sensors. Two correspondingchannels are connected at their output to a logic phase detector, fromwhich the resulting signal is characteristic of the phase shift betweenthe signals provided by the assembly of two sensors in question. In thecase of the vectorial process described above, the two phase shiftsderived from the four sensors are combined so as to reconstruct thedesired vector.

The device is designed in such a way that the leakage current towardsthe patient is maintained within statutory limits (for example:exclusive power supply by accumulators, use of isolation amplifiers oroptical couplers).

Each amplifier is protected by a limiter from voltage surges which maybe produced by equipment used simultaneously by the operator.

When a ventricular tachycardia is not spontaneous, it is necessary toinduce it by an impulse generator known as an "external cardiacstimulator", connected to the heart by conductor electrodes. In orderfor the present device to preserve its capacity to operate, it isnecessary to insert an analogue switch in the measuring chain,controlled by the impulses of the stimulator.

All the signals derived from the circuits described are conveyed to aninterface means between the device and the operator, employing one ofhis physiological senses, namely sight, hearing, touch, which indicatesto him:

on the one hand, either the sense and direction in which the myocardialdepolarization is propagated, or the sense and direction in which theprobe must be moved in order to carry out the next stage of acquisition;

on the other hand, where appropriate, the absence of a phase shift inall directions, and hence the localization of the emergence point underthe position concurrently occupied by the probe; this result authorizesthe use of the means of destruction integrated in the azimuthal probe,or any other external device provided by the user.

The functions carried out by the wired electrical circuits describedabove are carried out, in another version of the device, by a computerreceiving the signals derived from the sensors after amplification, andcarrying out similar functions of the device, to the extent that thelatter are programmed. This computer is provided with its peripheralsfor an analogue-to-digital conversion and interface with he user.

FIGS. 1a and 1b show embodiments, given by way of example, of the end ofthe probe in the basic version of the device according to the invention;in "a" the epicardial probe, in "b" the endocardial catheter.

FIG. 2 shows, in section, the wall of the heart containing the seat ofactivation and the corresponding emergence points.

FIG. 3 shows, in "a" the propagation of the cardiac depolarization fromthe emergence point, and in "b" a pathway of the depolarization wavewith two stages of measurement carried out with the device.

FIGS. 4a and 4b show embodiments, given by way of example, of the end ofthe probe in improved versions.

FIG. 5 shows the four signals derived from the vectorial version of thedevice, grouped in pairs, producing the two phase shift values afterprocessing.

FIG. 6 shows the reconstruction of the depolarization vector using theabove two phase shifts.

FIG. 7 shows this vector superposed on the position concurrentlyoccupied by the probe, and the directions and senses in which theoperator must move the probe in order to carry out the next stage ofacquisition.

FIG. 8 shows the block diagram of the basic electronic circuits used inthe device.

FIG. 9 shows the block diagram of the means of elimination of theimpulses originating from the external cardiac stimulator.

FIG. 10 shows the block diagram of the device/operator interface.

FIG. 11 shows the block diagram of the programmed version of the device.

FIG. 12 shows the limiter designed to protect the amplifier from voltagesurges.

FIG. 13 shows, in section, an embodiment of the needle-probe given byway of example, with the arrangement of the electrodes, of the activeportion of the means of destruction located on the needle-probe and ofthe generator which is associated therewith.

FIG. 14a shows an embodiment, given by way of example, of thedevice/user interface, preceded by the detector corresponding thereto.FIG. 14b shows the arrangement of the indicator lamps on the probe, thecontrol of which is performed by the circuit of FIG. 14a.

In FIGS. 1a and 1b, the examples of a probe comprise two sensors (1) and(2), arranged on an approximately rectilinear axis (3), attached to asupport (7) and equipped with electrical conductors (4) and (5), whichare themselves contained in a cable (6) which conveys the signals to beutilized by the electronic circuits of the device.

FIG. 2 shows, in a portion of myocardium (8) in section, the seat ofactivation (12) of the ventricular tachycardia, and its electricalprojections (12') and (12") on the epicardium (9) and on the endocardium(9'), that is to say the emergence points. The line (10) shows anexample of a pathway followed by the myocardial depolarization from theseat of activation (12).

FIG. 3a shows a heart (15), comprising an epicardial emergence point(12'), producing centripetal depolarizations (13) which vary in speed inaccordance with the local conduction conditions. The curves for equalintervals of depolarization from the point (12') are known as isochrones(14).

FIG. 3b shows a detail of FIG. 3a, locating an arbitrary starting point(16) when the device according to the invention is used, as well as thefirst stage (17) located at a distance (18) from the starting point. Thedistance (18) depends on the operator's experience. It will be smaller(a few millimeters) for a beginner. The orientation of the point (17)relative to (16) is determined in accordance with the indications of thedevice when it is at (16).

The description which follows gives an example of an embodiment of thedevice according to the invention. The working end of the probe is shownin FIGS. 4a and 4b. Two assemblies of two sensors (1), (2) and (1'),(2') are arranged at right angles according to two axes (19) and (20) ona support (7). The sensors are less than 50 millimeters apart. Thisdistance is inversely proportional to the capacity of the circuits todiscriminate the phase shift of the signals, dependent on the bulktolerated for the probe and proportional to the precision required ofthe device. Each sensor is, in the present case, composed of twoelectrodes each connected to an input of the instrumentation amplifier,the input impedance of which is adjustable. The spacing of theelectrodes and the impedance must be sufficiently low to separate thelocal potentials from the remote potentials generated by the myocardium,given that excessively low spacing and impedance values no longer enablesignals of sufficient amplitude to be recorded. A probe having anadditional two assemblies of two sensors (1"), (2") and (1'"), (2'")arranged according to two additional axes (21) and (22), is shown inFIG. 4b.

A few tests of probes of different sizes enable the best compromise tobe found.

The signals (23), (24) and (26), (27) derived, respectively, the sensors(1), (2) and (1'), (2') and shown in FIG. 5 are compared, in pairs, fromthe standpoint of their phase, resulting in phase shift signals (25) and(28).

In FIG. 6, the algebraic values of these phase shifts are transferred toan orthonormal reference system (30) and (31). These two segmentsrepresent the projections, in the plane of the probe support (7), of avector (29) which can be superposed on the direction and sense of themyocardial depolarization. The trigonometric angle α formed with thepositive semi-axis (29) is calculated by: ##EQU2## where: τ₁ =delay (23)τ₂ =delay (26)

and: (τ₁, τ₂)εR²

The angle is the so-called "azimuth" of the depolarization at the pointwhere the probe is located.

In FIG. 8, the signals are processed by wired analogue and digitalelectronic circuits comprising, per sensor (1) or (2):

an amplifier (34) or (34') which brings the signal to a voltage and animpedance compatible with the following circuits,

a filter (35) or (35') designed to select the useful portion of thesignal,

a hysteresis comparator (36) or (36') which converts the signal to aform which can be utilized by logic circuits.

The two resultant outputs (37) and (38) are compared by a phase detector(39) which produces a signal (40) characteristic of the phase shiftbetween the events detected by (1) and (2). The two lines (37) and (38)convey the signals (23) and (24), respectively, of FIG. 5. The line (40)conveys an impulse which corresponds to the delay (25) in FIG. 5. Thisdelay has a value measured in milliseconds, and has an algebraic signdepending on whether (24) is ahead of or behind (23).

The circuit shown in FIG. 8 has to be duplicated in order to process thesignals derived from the sensors (1') and (2') of FIG. 4a. This resultsin two phase shift signals (40) and (40').

In FIG. 10, the operator (44) is provided with the azimuth indication byan interface means (43) collecting the phase shift signals (40) and(40') derived from the two phase comparators (39) and (39').

A simple example of embodiment of the interface is given in FIG. 14a.The signals (38), via a monostable (53) set at 50 ms and triggered bythe rising and falling fronts, and (37) control a flip-flop D, thecomplementary outputs Q and Q of which adopt a 0 or 1 logic levelaccording to the order of appearance of the signals at the input. Two ofthe four light-emitting diodes (55), (56), (57) and (58) are illuminatedto indicate the azimuth from which the depolarization originates. Theoperator moves the probe accordingly in this direction and sense inorder to perform the next stage of acquisition.

In FIG. 9, if it is used, an external cardiac stimulator connecteddirectly to the input (42) is used to control an analogue gate (41)blocking or otherwise the signals originating from the probe. In theabsence of an impulse, the switch (41) is closed and allows the signalsoriginating from the sensor (1) to pass through. During the impulse, theswitch (41) is open and prevents the signal corresponding to theimpulse, which is conducted by the heart, from interfering with theoperation of the device.

In FIG. 12, the amplifier (34) is protected at its input, by a limiter(45), against voltage surges which are introduced by devices which theoperator may use in proximity to the probe (for example: electricscalpel, defibrillator).

FIG. 13 shows the localization, on the needle (32) for example, of theactive portion (51) of the means of destruction of the seat ofactivation (12) of the ventricular tachycardia.

In a second version of the device shown in FIG. 11, the electroniccircuits are produced using programmed logic technology, carrying outfunctions similar to the wired version and comprising sensors (1), (2)and (1'), (2') connected to amplifiers (34), (34') and (34"), (34"'),followed by analogue-to-digital converters equipped withsampling/blocking units (46), (46') and (46"), (46"'), and a programmedprocessor (47) which carries out the acquisitions, filters andrecognizes the signals, compares them and indicates to the operator (44)via the interfaces (48) and (48') the procedure to be followed in orderto reach the emergence point. The processor (47) also carries out, whereappropriate, the elimination of the stimulatory impulse in theprocessing of the signal. The four conversion systems (46), (46'), (46")and (46"') may be replaced by four sampling/blocking units, followed byan analogue multiplexer, followed by a single analogue-to-digitalconverter.

I claim:
 1. An apparatus for localizing an emergence point of aventricular tachycardia in a heart, comprising:a probe including atleast two sensors for contacting surface portions of the heart anddefining a substantially rectilinear axis; electronic monitoring meansfor receiving electrical signals from the sensors, and for processingthe electrical signals received from the sensors to determine a senserelative to the rectilinear axis and a direction of the emergence point,including means for measuring a phase shift between the electricalsignals received from the sensors; and display means for receiving theprocessed electrical signals from the monitoring means, and fordisplaying the received, processed electrical signals to an operator ofthe apparatus; wherein the processed electrical signals displayed by thedisplay means indicate the sense and the direction of the emergencepoint relative to propagation of a myocardial depolarization.
 2. Theapparatus of claim 1 wherein the phase shift measuring means includesmeans for making plural phase determinations, and means for indicatingthe direction of the emergence point responsive to said plural phasedeterminations.
 3. The apparatus of claim 2 wherein the means for makingplural phase determinations operates responsive to rotations of theprobe about an axis perpendicular to the surface of the heart.
 4. Theapparatus of claim 3 having means for measuring a maximum phase shiftbetween the signals received from the sensors, for indicating when theemergence point lies in the direction of the rectilinear axis.
 5. Theapparatus of claim 3 having means for measuring a phase shift betweenthe signals received from the sensors which approaches zero, forindicating when the emergence point lies in a direction perpendicular tothe rectilinear axis.
 6. The apparatus of claim 3 having means forlocalizing the emergence point responsive to successive movements of theprobe.
 7. The apparatus of claim 6 wherein the localizing means includesmeans for measuring a zero phase shift in all directions.
 8. Theapparatus of claim 6 wherein the sensors are separated by less than 50millimeters.
 9. The apparatus of claim 1 wherein the probe has two pairsof sensors defining two axes on the probe.
 10. The apparatus of claim 9having means for electrically combining the electrical signals from thesensors in said monitoring means to define an azimuth indicating thesense and the direction of the emergence point.
 11. The apparatus ofclaim 10 wherein the axes are substantially perpendicular to each other.12. The apparatus of claim 11 wherein the paired sensors produce paired,phase-shifted signals, and wherein the monitoring means includes meansfor developing a vector indicating the sense and the direction of theemergence point responsive to a paired, phase-shifted signals of thesensors.
 13. The apparatus of claim 1 wherein the probe further includesa needle for progressive introduction into the myocardium, forlocalizing the seat of activation of the ventricular tachycardia. 14.The apparatus of claim 13 wherein the probe includes a means fordestroying the emergency point.
 15. The apparatus of claim 1 wherein theelectronic monitoring means comprises a plurality of amplifierselectrically connected to the sensors, a corresponding plurality offilters electrically connected to the amplifiers for selecting a desiredfrequency component of the electrical signals received from the sensors,and a corresponding plurality of hysteresis comparators electricallyconnected to the filters for producing logic signals for application tothe display means.
 16. The apparatus of claim 15 which further comprisesa logic phase detector for receiving said logic signals from thehysteresis comparators and for producing a signal characteristic of aphase shift between the electrical signals provided by the sensors. 17.The apparatus of claim 16 which includes means for isolating theapparatus from external leakage currents within specified limits. 18.The apparatus of claim 17 which includes a limiter coupled with theamplifiers for protecting the amplifiers from voltage surges which areproduced by other equipment used by the operator.
 19. The apparatus ofclaim 17 which includes an analog switch coupled with the amplifiers foreliminating signals originating from a cardiac stimulator through themyocardium.
 20. The apparatus of claim 19 having means for controllingthe analog switch responsive to electrical impulses received from thestimulator.
 21. The apparatus of claim 1 wherein the display meanscomprises an interface between the apparatus and the operator, foremploying a physiological sense of the operator.
 22. The apparatus ofclaim 1 wherein the electronic monitoring means includes a plurality ofamplifiers for receiving the electrical signals from the sensors,sampling means for receiving amplified signals from the amplifiers,analog-to-analog conversion means coupled with the sampling means, and acomputer coupled with the analog-to-digital conversion means and thedisplay means.
 23. A method for localizing an emergence point of aventricular tachycardia in a heart, comprising the steps of:contactingsurface portions of the heart with a probe including at least twosensors defining a substantially rectilinear axis; monitoring electricalsignals received from the sensors, and processing the monitoredelectrical signals to determine a sense relative to the rectilinear axisand a direction of the emergence point, including measuring a phaseshift between the electrical signals received from the sensors; anddisplaying the processed electrical signals to an operator, indicatingthe sense and the direction of the emergence point relative topropagation of a myocardial depolarization.
 24. The method of claim 23which further includes making plural phase determinations, wherein thedirection is indicated responsive to said plural phase determinations.25. The method of claim 24 wherein the plural phase determinations aremade by rotating the probe about an axis perpendicular to the surface ofthe heart.
 26. The method of claim 25 which further includessuccessively moving the probe until the emergence point is localized.27. The method of claim 26 wherein the emergence point is localized whena zero phase shift is measured in all directions.
 28. The method ofclaim 26 which further includes defining an azimuth indicating the senseand direction of the emergence point by electrically combining signalsreceived from the sensors.
 29. The method of claim 26 which furtherincludes progressively introducing a needle associated with the probeinto the myocardium to localize the seat of activation of theventricular tachycardia.
 30. The method of claim 29 which furtherincludes destroying the emergence point.
 31. The method of claim 26which further includes eliminating signals originating from a cardiacstimulator through the myocardium.
 32. The method of claim 31 whereinthe cardiac stimulator signals are eliminated responsive to electricalimpulses received from the stimulator.
 33. The method of claim 26 whichfurther includes interfacing with the operator, for employing aphysiological sense of the operator.
 34. The method of claim 25 whichfurther includes measuring a maximum phase shift between the signalsreceived from the sensors, indicating when the emergence point lies inthe direction of the rectilinear axis.
 35. The method of claim 25 whichfurther includes measuring a phase shift between the signals receivedfrom the sensors which approaches zero, indicating when the emergencepoint lies in a direction perpendicular to the rectilinear axis.